The impact of 75 years of climate change on Mediterranean glacier mass balance

Few glaciers remain in the Mediterranean region: those that do have mostly retreated well into cirques, persisting as small, isolated glaciers or ice patches. In this study, we found that summer temperatures in the Mediterranean region have risen dramatically since the 1970s with the average increasing by >1.9 °C by 2024 relative to the 1991–2020 mean. Winter precipitation in the Mediterranean region has shown a statistically significant slight declining trend over the last 75 years. From 2019 to 2023, snow cover duration declined across most of the Mediterranean. The North Atlantic Oscillation (NAO) has a limited influence on glacier mass balance and snowpack in the Mediterranean based on results of regression analysis. This is because the dominant control on mass balance change in the Mediterranean is summer temperature rather than precipitation, much more so than further north in Europe where NAO has more influence on glaciers. However, local topoclimate factors mitigate the summer temperature impact allowing the paradox of glacier survival in niche settings in some of the wettest Mediterranean regions. Most Mediterranean glaciers only survive high summer temperatures because of excess snow accumulation by avalanching snow, highlighting the key influence of local topoclimatic conditions on glacier survival in the Mediterranean region. The fact that Mediterranean glaciers only survive because of high accumulation but are also strongly affected by changes in summer temperature, accords with the global observation that warm-wet glaciers are more sensitive to changing temperature than cold-dry glaciers. Understanding how glaciers and snowpack respond to climate change in the Mediterranean mountains has relevance beyond this region and provides an important comparison for other mid-latitude regions where glaciers and snowpack are crucial for water supply.